Martin Freeman as Bilbo Baggins in The Hobbit. The trilogy has been important for tourism in New Zealand.

A successful Middle- earth marketing campaign coupled with increased cruise ship and international flight capacity appears to be driving a resurgence in Western visitors to New Zealand, according to a new report.

The study, by the New Zealand Institute of Economic Research (NZIER) for Tourism New Zealand, found visitors from traditional Western advanced-economy countries surged more than expected last year.

Visitors from the United States grew 13.4 per cent - an extra 23,744 people - during 2013, but the report found that improving US economic conditions were not driving growth.

"Marketing effectiveness has likely been a key driver of visitor growth that cannot be attributed to global growth, air capacity or chance," the NZIER report said.

An increase in German visitors, up 9.5 per cent last year, was also mostly put down to improved New Zealand marketing.

The report, which was tasked with understanding the factors driving the increase in visitor numbers, largely dismissed the improving conditions in Western economies as a key factor.

"We find that economic factors matter but cannot explain all of the growth in visitor arrivals," the NZIER report said.

Tourism New Zealand chief executive Kevin Bowler said the results were surprising.

"Leveraging the movies will continue into 2015," Bowler said.

The final instalment of The Hobbit trilogy, The Hobbit: There and Back Again will be released in cinemas worldwide from December. "Lots of people would like to come to New Zealand and the Middle-earth campaign, which began 10 years ago with the Lord of the Rings, showcases the landscape in graphic detail and gives them the reason to come," Bowler said.

The report found the Middle- earth campaign was a factor in improving awareness of New Zealand. Penetration was highest in Britain but the campaign raised the opinion of New Zealand the most in the US. Bowler said Middle-earth was now a factor behind the decision of 14 per cent of visitors to come to New Zealand.

German and US visitors stay for longer and so spend more, he said, but visitors from Britain spend more here than in any other place, making New Zealand a premium destination.